Question

..x+y+z=7 y+z+u=15 z+u+x=11 u+x+y=9

Answer 1

解

已知

x+y+z=7 [1]

y+z+u=15 [2]

z+u+x=11 [3]

u+x+y=9 [4]

四个算式相加

3[x+y+z+u]=22+20

x+y+z+u=14

减去【1】

u=7

减去【2】

x=-1

减去[3]

y=3

减去【4】

z=5